I had posted on endless sphere but since then I have possibly made a little discovery.
Tldr; I have a fresh 48v battery and charger around less than 3 months old. Very intermittently when trying to charge the battery the charger will power up, the fan spins up and then it starts to make a nasty buzzing / whirring sound. Its pretty loud normally but this is something else.
My discovery since the last post is that I no longer believe this is a broken fan issue, as I know that can make a lot of noise. I will not dismiss the possibility by any means though. Main reason for believing this is that when I charge at home it boots up fine and lightly whirrs. But more often than not I have noticed when I am charging in my place of work, this weird sound starts like clockwork almost as soon as I turn it on.
I can be entirely sure of this but id say i cant remember it once doing it at home, but its happened around 10 times now in work. Sometimes it can charge fine even on the supply, it is kind of odd.
I have attached a picture of the charger and a video sample of the noise it makes.
It is a generic style chinese brand charger so criticise if you wish but this is brand new, CE and RoHS tested.
Any help or SUGGESTIONS FOR A NEW CHARGER using the bespoke connector it has would be GREATLY appreciated.
[Charger noise video] https://streamable.com/1kmpr